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On retrieving the attached plots, I am at lost to interpret a couple of features,

In the "time series area averaged of cloud fraction from cloud mask" plot, obtained by MODIS-Terra, how is it to be interpreted the sharp increase from 2015 onwards? (it does not show up at all in the equivalent MODIS-Aqua plot).

In the "time series area averaged of combined cloud optical thickness" plot, obtained by MODIS-Aqua, how is it to be interpreted the very marked minima at every February solstice, which appears in the global plot as well as for either hemisphere ? (it does not show up at all in the equivalent MODIS-Terra plot).

 

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  1. Answer to this question from a Subject Matter Expert at GSFC:

     

    “The Terra MODIS cloud mask trend: This is due to cross-talk in the several IR spectral channels used in the mask. This is an issue for both Collection 5 (C5) and C6 production streams. We have documented this on our web site under “Data Issues” (http://modis-atmos.gsfc.nasa.gov/validation_35.html#Top and the accompanying “impact” document link at the bottom of that section) as well as in our L3 time series browse imagery (http://modis-atmos.gsfc.nasa.gov/IMAGES/08_Timeseries.html, click on “cloud fraction”, go to the tropical latitude figure, place the mouse over “Terra”).

    The MODIS MCST group has provided a cross-talk correction that is still being tested by the cloud mask team. Hope to get it into reprocessing early next year.

     

    ~Jan/Feb minimum in Aqua MODIS cloud optical thickness: Our L3 time series browse imagery shows a cloud optical thickness minimum for the boreal winter months for ice clouds over land for ±60 ° (see link above, click on “cloud optical depth”, go to the ±60° time series). This has the largest annual cycle, i.e., ocean surfaces, liquid phase clouds, and other latitude zones in our browse have a much smaller cycle and are out of phase with the ice cloud time series. The user is looking at combined phase (liquid + ice) and looking at all latitudes/surfaces; this is a dangerous thing to do but I’d say the browse image is consistent.”